1. Field of the Invention
The present invention relates generally to head mounted displays; and, more particularly to a head mounted digital viewing system that minimizes issues of hyperstereopsis, crew station obscuration, and reduced through-canopy optical performance and allows the user to see in low light conditions.
2. Description of the Related Art
Analog night vision systems such as those known the night vision industry as the PVS-14, the PVS-7, the AN/PSQ-20 (for ground soldiers) and the AN/AVS-6 (for helicopter pilots) have been successfully used for quite some time. These devices use image intensifier tubes with microchannel plates, to amplify available light at night from stars, moon, and cultural lighting in the near infrared (600-900 nm spectral region). Users view the amplified image on a phosphor screen, which is magnified by an eyepiece lens.
Digital night vision systems generally using conventional optics and displays are now being considered for future helmet mounted display programs in multiple applications which will replace current analog systems. These digital night vision systems physically mimic existing analog night vision designs and mounting.
Many digital systems typically mount the sensors above or beside the eyes, or provide a direct view digital configuration, routing the imagery using conventional optics to the user's eyes. This places a significant amount of weight in front of the user's eyes, which can compromise head/neck biomechanics in the event of a crash, ejection or fall.
Putting the sensors above or beside the user's eyes changes their viewpoint location such that it is not directly in line with their eyes. Since aircraft cockpits are designed to be viewed from the so called “Design Eye,” displacing the sensor location may result in a pilot looking through a canopy strut or obstruction and the inability to see critical cockpit display information. While this offset may not have as much impact on a ground soldier, it is not compatible with aircraft cockpit design. In addition, a wide sensor separation causes a problem known as “hyperstereopsis” which can seriously compromise the pilot's ability to fly by erroneously exaggerating stereo depth perception.
Night vision image quality is limited by shot noise, ambient irradiance and the dynamic range of the intensifier tube. At low light levels, the noise sources can interfere with the user's perception. When the user switches their viewing perspective from light to dark areas, it is possible that they may miss seeing a critical object.
Commercial head mounted displays exist, have been patented, or otherwise disclosed, and have marketed under the brands: Vuzix Smart Glasses M100, Google Glass, MicroSoft Glasses, and Lumus OE-32. These display systems have transparent displays that are positioned to the side of the eye or substantially in front of the eye. Most of these include only a display interface. Google Glass includes a sensor; however, both the display and camera are positioned to the side of the eye. MicroSoft Glasses also includes a sensor positioned between the user's eyes.